How to make a snip appear?

[Kshitij Sachan]

I've been trying to render an OpenGL context using a gl-bitmap and then displaying that in a snip (to enable user input). I extended the image snip class and overrode the basic methods to draw, get-extent, etc. 

When I try to display my snip, I see nothing, but when I highlight over the snip with my cursor I can see the shape underneath! It's clearly rendering, and I can render the gl-bitmap by itself fine when it is not connected to a snip. What could possibly be making my snip appear white?

My two hypotheses are:
1) I didn't set up the snip-class% correctly. I have no clue what the purpose of this is (the documentation is challenging to follow here), and I don't know what argument to provide to `(set-classname "(lib ...)")` (what should replace the ...?)

2) I didn't override one of the relevant functions such as set-unmodified?

Here is my code (MakeGLSupport and drawAFrame are both calls to extern "C" functions I'm accessing using the FFI. They setup the triangles in OpenGL and render those triangles, respectively):

#lang racket

(require racket/gui/base

         ffi/unsafe

         ffi/unsafe/define)

;; ffi code

(define my-ffi (ffi-lib "/Users/kshitijsachan/Documents/geopipe/builddir/lib/Debug/libgldraw"))

(define-ffi-definer define-gltest my-ffi)

;; type def

(define _GLTest-pointer (_cpointer 'GLTest))

;; functions

(define-gltest makeGLTest (_fun _int _int -> _GLTest-pointer))

(define-gltest drawAFrame (_fun _GLTest-pointer -> _void))

;; global variables

(define screen-width 100)

(define screen-height 100)

;; gl code

(define gl-config (new gl-config%))

(send gl-config set-double-buffered #f)

(send gl-config set-legacy? #f)

(define gl-bitmap (make-gl-bitmap screen-width screen-height gl-config))

(define gl-dc (new bitmap-dc% [bitmap gl-bitmap]))

(define gl-context (send gl-dc get-gl-context))

(define opengl-snip (make-object image-snip% gl-bitmap))

;; bitmap

(define my-bitmap (make-bitmap screen-width screen-height #t))

(define my-dc (new bitmap-dc% [bitmap my-bitmap]))

(send my-dc set-brush "red" 'solid)

(send my-dc set-pen "black" 3 'solid)

(send my-dc draw-ellipse 1 1 98 98)

;; snip-class (THIS IS WHAT I HAVE A QUESTION ON)

(define scroll-snip-class%

   (class snip-class%

     (inherit set-classname)

     

     (super-new)

     (set-classname "(lib test-snip)")

     ;; not sure if necessary

     (define/override (read f)

       (define width-b (box 0.0))

       (define height-b (box 0.0))

       (send f get width-b)

       (send f get height-b)

       (new scroll-snip% [snip-width (unbox width-b)] [snip-height (unbox height-b)]))

     ))

(define scroll-snip-class (new scroll-snip-class%))

;; custom image-snip (THIS IS ALSO WHAT I HAVE A QUESTION ON)

(define scroll-snip%

  (class image-snip%

    ;; set up fields

    (init bit)

    (define snip-bitmap bit)

    (init-field [snip-width screen-width] [snip-height screen-height])

    ;; make image-snip

    (super-make-object snip-bitmap)

    ;; add ability to handle events

    (inherit/super set-flags get-admin set-snipclass)

    (set-snipclass scroll-snip-class)

    (set-flags (list 'handles-events))

    ;; override methods

    (define/override (get-extent dc x y w h descent space lspace rspace)

      (define (maybe-set-box! b v) (when b (set-box! b v)))

      (maybe-set-box! w snip-width)

      (maybe-set-box! h snip-height)

      (maybe-set-box! descent 1.0)

      (maybe-set-box! space 1.0)

      (maybe-set-box! lspace 1.0)

      (maybe-set-box! rspace 1.0))

    ;; there seems to be a problem when copying (snip looks white but can be seen when highlighted)

    (define/override (copy)

      (new scroll-snip% [bit snip-bitmap]))

    

    (define/override (draw dc x y left top right bottom dx dy draw-caret)

      (send gl-context call-as-current

      (lambda () (drawAFrame (makeGLTest screen-width screen-height)) gl-bitmap))

      (super draw dc x y left top right bottom dx dy draw-caret)

      )

    

    (define/override (on-char dc x y editorx editory event)

      (cond

        [(equal? (send event get-key-code) 'up)

         (define admin (get-admin))

         (set! snip-width (+ snip-width 15))

         (set! snip-height (+ snip-height 15))

         (when admin

           (send admin resized this #t))]

        [(equal? (send event get-key-code) 'down)

         (define admin (get-admin))

         (set! snip-width (- snip-width 20))

         (set! snip-height (- snip-height 20))

         (when admin

           (send admin resized this #t))]))

    ))

(new scroll-snip% [bit gl-bitmap])

Any help would be appreciated! I've been stuck on this for quite a while :)

[Kshitij Sachan]

Update:

I've narrowed down the problem to the `copy` method of the snip. When I delete the copy method, I can see the snip perfectly, but it can't be resized (because no copy method implemented).

I removed the GL component, so now I'm only attempting to extend the image-snip% class to resize a custom bitmap I load in (in my case just a plain red circle I drew). When I highlight over the snip with my cursor, I can see the bitmap below and it is resizing as well on a click (using `set-bitmap`). However, if I don't highlight over the snip it appears plain white.

Another observations that may or may not help is:

Calling (send s get-bitmap) always returns the bitmap of the same size, even if I've pressed on the snip several times to resize it.

Here's the simplified code:

(require racket/gui

         racket/gui/base)

;; bitmap stuff

(define bits (make-bitmap 250 250))

(define bits-dc (new bitmap-dc% [bitmap bits]))

(send bits-dc set-brush "red" 'solid)

(send bits-dc set-pen "black" 3 'solid)

(send bits-dc draw-ellipse 1 1 248 248)

(define snip (make-object image-snip% bits))

;; snip stuff

(define scroll-snip%

  (class image-snip%

    (init bit-init)

    (define snip-bitmap bit-init)

    (inherit/super get-admin set-flags set-bitmap)

    (init-field [w 100] [h 100])

    

    (super-make-object snip-bitmap)

    (set-flags (list 'handles-events))

    

    (define/override (get-extent dc x y width height descent space lspace rspace)

      (define (maybe-set-box! b v) (when b (set-box! b v)))

      (maybe-set-box! width w)

      (maybe-set-box! height h)

      (maybe-set-box! descent 1.0)

      (maybe-set-box! space 1.0)

      (maybe-set-box! lspace 1.0)

      (maybe-set-box! rspace 1.0))

    (define/override (on-char dc x y editorx editory event)

      (cond

        [(equal? (send event get-key-code) 'down)

         (define admin (get-admin))

         (set! w (+ w 20))

         (set! h (+ h 20))

         ;; brush/pen/draw ellipse

         (define new-bits (make-object bitmap% w h))

         (send bits-dc set-bitmap new-bits)

         (send bits-dc draw-ellipse x y (- w 2) (- h 2))

         (set! snip-bitmap new-bits)

         

         (when admin

           (send admin resized this #t))]

        [(equal? (send event get-key-code) 'up)

         (define admin (get-admin))

         (set! w (- w 20))

         (set! h (- h 20))

         ;; brush/pen/draw ellipse

         (define new-bits (make-object bitmap% w h))

         (send bits-dc set-bitmap new-bits)

         (send bits-dc draw-ellipse x y (- w 2) (- h 2))

         (super set-bitmap new-bits)

         

         (when admin

           (send admin resized this #t))]

        [(equal? (send event get-key-code) 'escape)

         (define admin (get-admin))

         (set! w 150)

         (set! h 150)

         ;; brush/pen/draw ellipse

         (define new-bits (make-object bitmap% w h))

         (send bits-dc set-bitmap new-bits)

         (send bits-dc draw-ellipse x y (- w 2) (- h 2))

         (super set-bitmap new-bits)

         

         (when admin

           (send admin resized this #t))]))

    (define/override (on-event dc x y editorx editory event)

      (cond

        [(send event button-down?)

         (define admin (get-admin))

         (set! w (+ w 20))

         (set! h (+ h 20))

         ;; brush/pen/draw ellipse

         (define new-bits (make-object bitmap% w h))

         (send bits-dc set-bitmap new-bits)

         (send bits-dc draw-ellipse x y (- w 2) (- h 2))

         (super set-bitmap new-bits)

         

         (when admin

           (send admin resized this #t))]))

    (define/override (draw dc x y left top right bottom dx dy draw-caret)

      ;; brush/pen/draw ellipse

      ;(define new-bits (make-object bitmap% w h))

      ;(send bits-dc set-bitmap new-bits)

      ;(send bits-dc draw-ellipse x y (- w 2) (- h 2))

      ;(set! snip-bitmap new-bits)

      (super draw dc x y left top right bottom dx dy draw-caret))

    (define/override (copy)

      (make-object scroll-snip% snip-bitmap))

    ))

(define s (make-object scroll-snip% bits))

s

I believe there must be a problem with the default implementation of the `copy` method, but I don't know enough to parse what's going on there. Here is the Racket source code implementation of an image-snip% https://github.com/racket/snip/blob/1a0ef3670ebb13e8738d838db167c3abdbf3df28/snip-lib/racket/snip/private/snip.rkt#L888.

[Alex Harsanyi]

I am not entirely sure why (because I already spent more than 15 minutes on this :-) ), but the problem is with the `get-extent` method: just remove it, and let `image-snip%` handle the method.

The `copy` method is not used in this case.

Also, in your `on-char` and `on-event` methods, you might want to pass back any un-handled events back to the editor's `on-default-event` and `on-default-char` methods, otherwise, you will notice that the editor stops responding to some events since your code discards them.

Alex.

[Robby Findler]

Maybe because get-extent in the super class vaches some information and that cache doesn't get maintained if you override the method.

Robby

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